Cathode-ray tube with secondary intensity control of cathode rays



Sept. 5, 1950 A. RUSTERHOLZ A ETAL 2,521,255

CATHODE-RAY TUBE WITH SECONDARY INTENSITY CONTROL OF CATHODE-RAYS Filed Dec. 24, 1947 3 Sheets-Sheet 1 Sept. 5, 1950 A. RUSTERHOLZ ET AL 2,521,255

CATHODE-RAY TUBE WITH SECONDARY INTENSITY CONTROL OF CATHODE-RAYS Filed Dec. 24, 1947 3 Sheets-Sheet 2 Sept. 1950 A RUSTERHOLZ ETAL Y 2,521,255

CATHODE-RAY TUBE WITH SECONDARY INTENSIT CONTROL OF CATHODE=RAYS 3 Sheets-Sheet 5 Filed Dec. 24, 1947 fi ju,

Patented Sept. 5, 1950 CATHODE -RAY TUBE WITH SECONDARY IN- TENSITY CON TROL OF CATHODE RAYS Alexander Rusterholz, Zurich, and Hans Jakob von Baeyer, Baden, Switzerland, assignors to Patelhold Patentverwertungs & Elektro- Holding A.G., Glarus, Switzerland, a joint-- stock company of Switzerland Application December 24, 1947, Serial No. 793,630 In Switzerland August 23, 1946 Section 1, Public Law 690, August 8, 194-6 Patent expires August 23, 1966 22 Claims. (Cl. 315 -30) This invention relates to cathode ray tubes which include electrodes for effecting a secondary control of the cathode ray, and to cathode ray switches for use in multiple channel communication systems. I

At the transmitting station, a pulse multiplex system requires a device which produces a series, in point of time, of mutually independent current pulses in a single out-going line, the magnitudes of the several current pulses of cyclically repeated groups being controlled by the modulation of the individual messages to be transmitted.

Thanks to their freedom from inertia, cathode ray switches are suitable for this purpose, the cathode ray periodically scanning the control devices of the different message channels. It is necessary, in this connection, that the changes in the control voltages of the several message channels produce the greatest possible change in the intensity of the electron beam as it moves in succession to the collector electrodes of the different message channels, or, in other words, that the control sensitivity dip dU.

(where in is the electron current to one collector electrode and Us is the control voltage) attains a large value.

Various methods are already known for a secondary intensity control of cathode rays, where the electron current per se issuing from the cathode remains constant and the intensity change occurs only shortly before the collecting electrode. This regulation of the electron current to the collecting electrode is designated secondary intensity control in the following specification and claims to distinguish from the primary control of intensity in the electron gun system producing the electron beam.

The control system of each message channel requires at least two electrodes, 1. e. a control electrode and a collecting electrode, the collecting electrodes of all. the channels generally being connected to a common out-going line. A cathode ray of current strength it produces a current is to the collecting electrode, its magnitude being dependent on the secondary control voltage Us in addition to being dependent on the initial beam intensity to, and

thus iF=J(2'n,Us). In case no appreciable space charge effects make their appearance (for example, with an initial current strength 50 of about 100 microamperes, none makes it appearance), the output current ir will be proportional to 2'0,

2 that is z'F=io.f(Us). The attainable control sensitivity di dU.

is then also proportional to in under this condition, and a constant primary current strength to of microamperes is assumed in the following discussion of control sensitivity. w,

The simplest control of the intensity of the cathode ray striking a collector electrode is obtained by deflecting the ray with respect to a diaphragm or apertured baille by electrical or magnetic fields transverse to the direction of travel of the electrons, thereby trapping more or less ofthe electrons upon the baffle to prevent theirimpact upon the collecting electrode. The control sensitivity of an arrangement of this kind amounts to about 1.33-10- amperes per volt. This relatively favorable control sensitivity is produced however by an electrode system very extensive in space; and a single cathode raytube for a communication system with twenty or more message channels would be too large to be practical.

It is also known that a change in the potential of the collector electrode will vary the counter field in advance of the collector electrode, and thereby vary the electron current to the collector electrode. The control sensitivity of such a system may be of the order oi 10- amperes per volt. Unfortunately, however, this high control sensitivity can not be attained in a cathode ray switch of a multiplex communication systemsince the voltage on the collector electrode affects the electron current and it therefore is impossible to connect the collector electrodes of all message channels to a common transmission line.

Another method of sensitivity control permits the entire electron ray to reach the collector electrode through an apertur in a control electrodeadiacent the electron gun side of the. collector electrode, and regulates the effective output current by controlling the secondary electron current liberated by impact of the electron' ray upon the collector electrode; The secondary electrons released from the primary current on the collector electrode travel to the controlelec:

trode or return to the collector electrod according to the amount and sign of the potential difference between the.contro1 electrode and the collector electrode; theimagnitude of the collector-electrode current being determined in this Way. The-control sensitivity of this arrangement hasgga magnitude. of, 5. 07 1 amperes. .per

volt when the collector electrode is suitably positioned with relation to the electron ray. With vertical incidence of the electrons on the collector electrode, a mean value of 0.5-10- amperes per volt is to be expected. Thi method has the drawback, however, that not only may the primary current itself release secondary electrons, but also secondary electrons reaching the collector electrode at an angle produce further secondary electrons in their turn and thus have a harmful influence on the original electron stream z' It will be shown later that the control device according to the invention does not have this drawback.

According to this invention, the control of the cathode ray intensity at the collector electrode is efiected by a retarding electrical field along the cathode ray path, the retarding field having the characteristics of a so-called potential saddle. If a plane is passed through the axis of the oathode ray, and a plot of potentials at points along the axis develops a curve which drops to a point at or adjacent the axis and then rises, i. e. is saddle shaped, the electrical field is said to be of the potential saddle type. This retarding field is not open to the objection of the homogeneous retarding field of the previously described control method which required a change in the potential of the collector electrode. The potential saddle is developed in front of the collector electrode (upon which a constant energizing potential is maintained) by an auxiliary electrode or electrodes which are outside the path of the electron ray and take the form of the diaphragms with circular or rectangular openings.

The point of minimum potential along the cathode ray axis is termed the saddle point" and, when the saddle point potential is approximately equal to the cathode potential, some of the electrons which approach the saddle point at high speed may pass beyond to reach the collector electrode. The number of electrons which arrive at the collector electrode varies with the saddle point potential and a mathematical analysis indicates that the control sensitivity for electrons at the axis of the ray, i. e. for a cathode ray of infinitesimally small crosssection, is of the high order of 0- amperes per volt which is obtained with the homogeneous opposed field method.

Since, however, it is not possible to compress an electron beam of non-disappearing current strength to an infinitesimal cross-section, special considerations are to be observed in constructing the control system in order to attain with certainty a relatively high or maximum control sensitivity.

The invention relates to a cathode ray tube in which a secondary intensity control of cathode rays is obtained by changing the potential of the saddle point of the electrical ontrol field between an accelerating electrode and a collector electrode and, more specifically, to a cathode ray tube with at least one control system comprising a retarding electrode and a control electrode arranged between the accelerating electrode and the collector electrode.

Objects of the invention are to provide cathode ray tubes which afford a secondary intensity control of high sensitivity with control electrode systems of small dimensions which are well adapted for incorporation in cathode ray switches for use in multiplex communication systems. Objects are to provide cathode ray tubes and cathode ray switches for use in multiplex communication systems in which a secondary intensity control is efiected by a retarding electrical field of the potential saddle type. An object is to provide a cathode ray tube or cathode ray switch in which a secondary intensity control is obtained, and without altering the energizing potential impressed upon a collector electrode or collector electrodes, by a control system including an apertured retarding electrode and an apertured control electrode between an accelerating electrode and the collector electrode.

These and other objects and the advantages of the invention will be apparent from the following specification when taken with the accompanying drawings in which:

Fig. 1 is a schematic perspective view of an electron gun and an associated secondary intensity control system embodying the invention;

Fig. 2 is a curve sheet showing the potential saddle characteristic of the electrical field established by a control system as shown in Fig. 1;

Fig. 2a is a curve sheet, on a greatly enlarged scale, of the potential saddle characteristic in the immediate region of the saddle point;

Fig. 3 is a curve sheet showing the potential variation in a plane transverse to the axis of the electron ray at the saddle point;

Fig. 4 is a longitudinal section, on an enlarged scale, of the electrode system of Fig. 1;

Fig. 5 is a schematic perspective view, with parts broken away, of the electrode system of a cathode ray switch embodying the invention;

Fig. 6 is a perspective view of another form of control and collector electrode system;

Fig. '7 is a schematic diagram of a multiplex communication system including cathode ray switches embodying the invention; and

Fig. 8 is a schematic diagram of a cathode ray switch for a two-way communication system of the multiple channel type.

The basic arrangement of a control system is shown schematically in Fig. 1. A cathode K and electron gun G develop a cathode ray R which may be directed in the plane YZ by deflecting electrodes or plates P to pass centrally through the opening of an accelerating electrode A which has a high positive potential, the potential of the cathode K being zero. The electron path beyond the electrode A is through a slotted retarding electrode B and a slotted control electrode S to the collector electrode F. The retarding electrode B has a fixed negative potential such that the electrons reach the neighborhood of the control electrode S in greatly retarded condition, and the number of electrons which can pass through the control electrode to reach the collector electrode F depends upon the instantaneous magnitude of the negative potential impressed upon the control electrode. A constant positive potential is impressed upon the collector electrode, but its magnitude is small in comparison with that applied to the accelerating electrode A.

It is to be noted that the four electrodes are drawn to a scale which is greatly enlarged with respect to the spacing of the collector electrode from the cathode K, and that a plurality of similar sets of four electrodes will be included in a tube which functions as a cathode ray switch in a multiplex communication system. The function of the deflecting electrodes P in such a tube is to deflect the cathode ray R in succession to the several sets of electrodes.

In Fig. l, the potential distribution in the electrical field which determines the intensity of the cathode ray at the collecting electrode F is plotted with respect to the plane YZ and appears. as a saddle-shaped surface PS. The potential distribution between the cathode K and acc lerating electrode A does not affect the secondary intensity control and therefore only the potential saddle surface PS between electrodes A and F! is illustrated. The saddle point T is located as nearl as possible in the plane of the control electrode S by a suitable choice of the electrode spacings, the slot dimensions and the electrode potentials.

The variation of potential Uz of the field in the plane YZ passing through the saddle point T is shown in Fig. 2, and the hatched portion beneath the curve Uz, which portion indicates the field between the control electrode S and collecting electrode F which has a positive potential with respect to the cathode potential, is shown in a greatly enlarged scale in Fig. 2a. The potential distribution Uy in the plane XY through the saddle point T is shown in Fig. 3. In these curve sheets, the potential unit U is the value U A of the positive potential applied to the accelerating electrode A, and the length unit L is such that the mutually equal spacing of the electrodes A, B, S and F is 1011- length units L. The zero point of the Z axis in Figs. 2 and 2a is at the collector electrode F.

According to the invention, the retarding electrode B serves for greatly retarding the electrons in front of the control electrode S and thus to control the electrons in the neighborhood of the control electrode S by a flat potential saddle, whereby a satisfactory control sensitivity of the order of at least 0.5-- amperes per volt can be obtained. For this control sensitivity it has been demonstrated to be especially advantageous to focus the cathode ray at least approximately at the saddle point T by already known means such as electron lenses. A

A typical example of appropriate dimensions for a control electrode system embodying the invention and conforming to potential saddle surface PS is shown in Fig. 4. The arbitrary unit of length L is employed to indicate dimensions since only the ratios of the geometric measurements are important for the best control sensitivity. If the electrode spacing units L, then half the slot width SA of the anode A must equal 71.5L, and half the slot width SB=Ss of the retarding electrode B and the control electrode S must equal 19.61,. The mutually alike electrode spacings are thus related to the full width ZSA of the slot opening 4 of the accelerating electrode Am the ratio of 2:9, and are related to full widths ZSB, 28s of the slot openings of the retarding electrode B and the control electrode S respectively in the ratio of 4:5.

If Us designates the potential of the accelerating electrode A and the potentials of the other electrodes are similarly designated as UB, Us and Up respectively, then the best potential curve is obtained when UAI UB I Us 1 UF=1 0.084: -0.084 0.024

for the complete blocking of the cathode ray. If the ratio UazUs is made equal to 1:0.062, the cathode ray is let through completely. The saddle point then has a potential UT that bears the relation of +0.005:1 to the potential Us of the accelerating electrode. A.

This. potential ,distribution corresponds exactly to the potential curves shown in Figs. 1-3.

. The field potential at a point in the plane Yjz; and spaced from the saddle point Tbya distance y measured. in the .XY plane throughpoint T (see .Fig.,3) may be computedby the equation 7 where UT is the potential at the saddle poin t the plane XZ, as shown by, CUI'VGIUZ of Fig. 2, ,is

that Uz', the first derivative of curve Uz be zero at the transverse plane XY through the saddle point T, i. e. that a line tt tangent to the curve Uz, seeFig. 2a, be parallel to the Z axis, and that the second derivative Uz be greater than zero but as small as possible. These conditions are satisfied when the potentialcurve U2 is relatively flat in the region of the saddle point T. o V

The control system according to the invention is to be given such dimensions in practice that r the entire width 2S of the slot of the control electrode S is of the order of 2 mm. In agreementwiththe above statements as to arbitrary dimensionunits L, the entire slot width ZSA. of the accelerating electrode will be about 7.3 mm. and that of the retarding electrode B will be 2 mm; and the spacings di=d2=d3 of the electrodes willbe about'1.6 mm. If the potential of the accelerating electrode A of this arrangement is selected as +2000 volts (cathode potential equal to zero) the potential of the retarding electrode will be 168 volts and that of thecollector elec: trode F, will be +48 volts. For blocking, the system, the control electrode S must be brought to 168 volts, and for complete freedom of a cathode ray focussed on the saddle point T, the potential of the control electrode must be -1 25 volts.

Experiments have shown that by the control system according to the invention, the abovementioned sensitivity of the secondary electron control of 0.5-10- amperes per-volt can easily be surpassed with, at the same time,'practically complete prevention of the disturbances from electrons reaching collector electrode F at an angle. The electrons which arrive at the control system at a great angle of incidence in relation to the z axis are, in practically all cases, definitely prevented from passing by the potential saddle. Only electrons incident near the axis and along paths at, a small angle to the axis can pa ssto arrange the control systems accordingto Fig. 5

in two parallel groups .I and II located one'be- 7 hindtheother withappropriate.axialspacing.

In group I for example, twenty-four control elements such as shown by one only in Fig. 1 are brought together and in group II, twenty-five. The two accelerating electrodes A1 and A2, the two retarding electrodes B1 and B2, and the two collector electrodes F1 and F2 are there constructed as unitary electrodes in each group, a corresponding number of slot openings being provided in the accelerating electrodes A1 and A2 and in the retarding electrodes B1 and B2, and specifically according to the dimensions prescribed in connection with Fig. 4. The control electrodes S1 and S2 of the two groups I and II are constructed as individual elements for each message channel but are all located in one or the other of two control electrode planes.

The several control units of the groups I and II are arranged in lines indicated by numerals I to 5, and in columns marked a to e in group I and f to k in group II. There is no control unit at the central point, line 3 and column 0, of group I since the electron ray R from cathode K must pass freely through the group I control units to reach those of group II. The central openings ll of the accelerating electrode A1 and retarding electrode 131 are preferably substantially larger than the corresponding openings of the control units, and the collecting electrode F1 is similarly provided with a relatively large central opening. Defiecting plates P1 are provided between the electron gun G and the group I assembly to efiect a cyclic scanning of the several control units. The scanning voltages impressed upon the plates P1 are developed by a saw-tooth generator [2 and transmitted to the plates P1 over leads l3 and a switch I l which is ganged to a switch I 5, as indicated by dotted line 55, by which the scanning voltages of leads !3 may be transferred through leads II to deflecting electrodes P2 located between the group I and group II assembly of control units. The switches Id, I5 are controlled by a relay [8 which is cyclically energized by the generator 12 to open switch [4 and close switch i5 at the completion of the scanning of the group I control assembly. The switching system also includes means for controlling the focussing of the electron ray R in the region of the control electrodes of the two groups of control assemblies. As illustrated, the switch It has a third blade i l for closing the circuit of an auxiliary device, specifically an electron lens [9, which changes the normal focus of the beam as determined by the electron gun G or a main lens, not shown, from the group II to the group I assembly.

As illustrated in Fig. 5, the deflecting plates P2 are energized to sweep the electron ray R over the control units of group II, and the electron ray is shown as incident upon the control unit 4g at line 4 and column 9 of the group II assembly. The intensity of the electron beam incident upon the collecting electrode F2 is then determined by the modulating voltage impressed upon the control electrode of of the 4g system. Upon completion of the scanning of the group II assembly the relay I8 is deenergized and the switch it is closed for a repetition of the scanning of the group I control systerns. In place of the focussing coil IS, an equivalent circuit may alter the voltage impressed upon a focussing element, not shown, of the electron gun assembly G to shift focus of the ray R back to the group I assembly.

As shown in Fig. 6, each control unit may.include two retarding electrodes B and B in place of the single retarding electrode oitheFigs. l

and 5 constructions. The additional electrode makes it possible to lessen the eifect which the accelerating potential on electrode A has upon the field strength and shape of the potential saddle in the critical region of the saddle point. The voltages impressed uponthe retarding electrodes B and B may be such, for example, that the potential falls off greatly from the accelerating electrode A to the first retarding electrode B, and only slightly from that electrode to the second retarding electrode B. In Fig. 6 the openings through the electrodes A, B, B and C are circular in place of the rectangular or slot openings of the Fig. 1 control system, but this does not affect the qualitative character of the control system.

The general arrangement of a multiple channel radio communication system employingcathode ray switches according to the invention is shown schematically in Fig. 7. The cathode ray tubes ZDT and 26R at the transmitting station and the receiving station, respectively, may be and preferably are of identical construction. Only three control systems H 21 and 2| are shown in the tube 213T, it being understood that the number a: of control systems will be relatively high, for example x=25 if the cathode switch tube is provided with a single group of control systems arranged in lines and columns according to the group II assembly of Fig. 5. The collector electrodes F of all control systems of tube 211T are connected through lead 22 and resistor 23 to a source of positive potential +UF. Each collector electrode F is connected to its control electrode S through a blocking condenser 24 and the secondary winding of one of the audio frequency transformers 25 25 25 in the several message channels indicated by the arrows N N N. The several control electrodes S are connected to a source of negative potential Us through their individual transformer windings and a common lead 26. For simplicity, the leads for impressing working potentials on the accelerating electrodes A and retarding electrodes B are not shown.

The electron ray R developed by cathode K of the electron gun G is deflected by voltages impressed upon plates P, in known manner and by known means, to scan the control systems in repeated cycles. At the instant illustrated in Fig. '7, the electron ray passes. through control system 21 of the message channel N and a current pulse, which depends as to amplitude upon the instantaneous magnitude of the modulating voltage of channel N flows through the resistor 23. This current pulse can be taken off by lead 21 as a voltage pulse from the resistor 23, and, after amplification in amplifier 28, may impose an amplitude modulation upon a carrier frequency wave developed in transmitter 29 for radiation from antenna 38. Preferably, however, the amplitude-modulated voltage pulse from amplifier 28 is transformed to a frequency or time modulated pulse in a transmitter 36.

Pulses in sequence from the several message channels are thus transmitted from the antenna according to the selected scanning program.

The pulse sequence arriving at antenna 3| of the receiving station is amplified and demodulated by an amplifier-demodulator 32 and impressed upon the control electrodes S of all of the control systems 33 33 33 The primary windings of a series of audio transformers 34 34 34* of message channels N1, N2 N1; are connected betweenithe-collector electrodes F of the several control systems and a common lead 35 to a source of positive potential +Ur. The initial negative voltage is imposed upon the control electrodes S through a common connection, through resistance 36, tothe voltage source Us. The electron ray R of the receiving tube 20R is synchronized with the electron ray R of tube ZElT, for example in known manner, by transmitting a synchronizing pulse over one mes sage channel, and the ray R of tube 20R, therefore goes to the control system 33 of message channel N2 at the illustrated instant. The current pulse delivered by the receiver message channel N2 to a loud speaker or telephone therefore carries the modulation developed in the message channel N at the transmitting station.

If a two-way telephone system is set up between two stations, it is possible at both stations to combine the cathode ray tube of the transmitter with the cathode ray tube of the receiver, as is shown schematically in Fig. 8. The plane of the drawing of this figure is perpendicular to the direction of travel of the cathode ray and, for simplicity, the accelerating and retarding electrodes are not shown. The control systems, arranged, for example, in a circle, have been presented as cylindrical casing segments running in the direction of the axis, for simplifying the drawing, while actually these electrodes are parallel to the plane of the drawing.

The several parts of the two-way communication system are identified by the same reference numerals as in Fig. '7. The outgoing message channels are indicated by the arrows N N N which point inwardly towards the corresponding control systems 2l H 21*, and the incomcoming message channels are indicated by the arrows N N, N which point outwardly from the associated audio transformers 34 34 34*.

The electron ray in the apparatus according to Fig. 8 alternately scans the control system for an incoming message and the control system for an outgoing message but other scanning programs are of course possible. Both stations of the twoway communication system are provided with a cathode ray tube such as shown in Fig. 8, and the scanning of the two tubes must be synchronized by known means to insure that a receiving channel is completed at one station when a transmitter channel is established at the other station. v

It is to be understood that the invention may be employed in other fields in which a great number of circuits are to be cyclically opened and closed in succession and where a high control sensitivity is required. The invention is not limited to the particular voltage values and ratios of voltage values above specified as providing a high control sensitivity. The voltage values may be varied according to the specified ratios when the several electrodes of the control system are evenly spaced and the electrode openings have the form of rectangular slots. Other ratios of voltage values will afford best results when the electrodes are not evenly spaced and/or when the apertures are not rectangular slots.

We claim:

1. In a cathode ray tube, the combination with means including a cathode to develop an electron ray, a collector electrode, an accelerating electrode adjacent the collecting electrode at the side thereof facing said ray developing means, said accelerating electrode being apertured for the passage of the ray therethrough, and electrode means located more closely adjacent to said electron ray-developing means than to said accelerating electrode to direct said electron ray through the aperture of said accelerating electrode, .ofmeans for, establishing an electric control field of potential saddle type between said accelerating electrode and said collector electrode to control the intensity of the electron ray arriving at the collector electrode; said field-establishing means including aretarding electrode and. a control electrode positioned. between said accelerating electrode and said collecting electrode,

said retarding electrode and controlelectrode being apertured for .passage of the ray therethrough, potential means to maintain said collector electrode and said accelerating electrode at relatively low and'relatively'high positive potentials respectively with respect to said cathode, potential means to bias said retarding and control electrodes negatively with respect .to said cathode to locate the saddle point ofthe electric field substantially at the plane of the control electrode, and a source of modulating potential connected effectively between said cathode and said'controlelectrode to vary the intensity of the electron ray incident upon the collector electrode.

2. In a cathode ray tube, the invention as recited in claim '1, wherein the negative bias potentials imposed upon the retarding electrode and control electrode make the potential of the saddle point of the electric field approximately that of the cathode.

3. In a cathode ray tube, the invention as recited in claim 1, wherein the potential of the electric field in the region of the saddle point satisfies the requirement that the first derivative of the field potential in the direction of the axis of the electron ray is zero, and the second derivative is small but greater than zero. 4. In a cathode ray tube, the invention as recited in claim 1, in combination with means. to focus the electron ray at substantially the plane of the control electrode.

5.'In a cathode ray tube, the invention. as recited in claim 1, wherein the apertures ofsaid retarding electrode andcontrol electrode are redtangular slot openings.

6. In a cathode ray tube, the invention as recited in claim 1, wherein the apertures of said retarding electrode and control electrode are circular openings.

7. In a cathode ray tube, the invention as re-, cited in claim v1, wherein theretarding electrode is positioned between the accelerating electrode and the control electrode.

8. In a cathode ray tube, the invention as recited in claim 1, wherein said field-establishing means includes a pair of retarding electrodes between said accelerating electrode and the control electrode.

9. In a cathode ray tube, the invention as recited in claim 5, wherein the retarding electrode is positioned between the accelerating electrode and the control electrode, the apertures of said retarding electrode and control electrode are rectangular slot openings and the path from the accelerating electrode to the collector electrode is divided into equal sections by said retarding and control electrodes.

10. In a cathode ray tube, the invention as recited in claim 9, wherein the ratio of the equal electrode spacings to the slot opening of the accelerating electrode is 2:9, and the ratio of the equal electrode spacings to the slot openings of the retarding and control electrodes is 4:5.

11. In a cathode ray tube, the invention as recited in claim 10, wherein for the complete blocking of the electron ray the potentials impressed upon the accelerating electrode and the collector electrode have the ratio 110.024, and the potential impressed upon the accelerating electrode has the ratio 1:0.084 to the potentials impressed upon both the retarding and the control electrode.

12. In a cathode ray tube, the combination with means including a cathode for developing an electron ray, accelerating electrode means having a plurality of apertures therethrough, electrode means for deflecting said electron ray to scan the apertures of said accelerating electrode means, collector electrode means adjacent said accelerating electrode means in the path of the electron ray as it passes through the respective apertures of said accelerating electrode means; of means for establishing an electric control field of potential saddle type along the several electron ray paths between apertures of said accelerating electrode means and said collector electrode means; said field-establishing means including for each aperture a retarding electrode and a control electrode positioned between said accelerating electrode means and said collector electrode means, each retarding and control electrode being apertured for .passage of the electron ray therethrough.

13. In a cathode ray tube, the invention as recited in claim 12, wherein said accelerating electrode means comprises a plate electrode having a plurality of apertures therethrough, and said collector electrode means comprises a plate electrode extending across the electron ray paths through the several apertures of the accelerating electrode means.

14. In a cathode ray tube, the invention as recited in claim 13, wherein the several apertures of said accelerating electrode means are alined in lines and columns.

15. In a cathode ray tube, the invention as recited in claim 12, wherein said accelerating electrode means comprises a plate electrode individual to each aperture thereof, and said collector electrode means also comprises a plate electrode individual to each aperture of said accelerating electrode means.

16. In a cathode ray tube, the invention as recited in claim 15, wherein all of said plate electrodes of said collector electrode means are connected to each other.

17. In a cathode ray tube, the invention as re- 12 cited in claim 15, wherein all of said control electrodes are connected to each other.

18. In a cathode ray tube, the invention as recited in claim 15, wherein one-half of the .plate electrodes of said collector electrode means are connected to each other, and that the control electrodes associated with the other one-half of said plate electrodes are connected to each other.

19. In a cathode ray tube, the invention as recited in claim 15, wherein the individual plate electrodes of said accelerating electrode means are arranged in a circle.

20. In a cathode ray tube, the invention as recited in claim 12, wherein said accelerating electrode means comprises a pair of plate electrodes each having a plurality of apertures therethrough and spaced at different distances from said cathode, said collector electrode means comprises a plate electrode adjacent the respective apertured plate electrodes of the accelerating electrode. means, the, set of accelerating and collector plate electrodes closer to said cathode having centrally located openings to pass the electron ray therethrough.

21. In a cathode ray tube, the invention as recited in claim 20, in combination with means for focusing the electron ray substantially in the plane of the control electrodes associated with the individual plate electrode of the accelerating electrodev means as the apertures thereof are scanned by the electron ray.

22. In a cathode ray tube, the invention as recited in claim 12, wherein said field-establishing means for each aperture of the accelerating electrode means includes a pair of retarding electrodes.

ALEXANDER RUSTERI-IOLZ. HANS JAKOB VON BAEYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Certificate of Correction Patent N 0. 2,521,255 September 5, 1950 ALEXANDER RUSTERHOLZ ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 10, line 62, for the claim reference numeral 5 read 1;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 28th day of November, A. D. 1950.

THOMAS F. MURPHY,

Assistant Gammz'ssz'oner of Patents.

Certificate of Correction Patent No. 2,521,255

' ALEXANDER RUSTERHOLZ ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 10, line 62, for the claim reference numeral 5 read 1 and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 28th day of November, A. D. 1950.

September 5, 1950 [sun] THOMAS F. MURPHY,

Assistant Gammzssz'oner of Patents. 

